title: A chondroitin synthase-1 (ChSy-1) missense mutation in a patient with neuropathy impairs the elongation of chondroitin sulfate chains initiated by chondroitin N-acetylgalactosaminyltransferase-1.
abstract: BACKGROUND
  Previously, we identified two missense mutations in the chondroitin N-acetylgalactosaminyltransferase-1 gene in patients with neuropathy. These mutations are associated with a profound decrease in chondroitin N-acetylgalactosaminyltransferase-1 enzyme activity. Here, we describe a patient with neuropathy who is heterozygous for a chondroitin synthase-1 mutation. Chondroitin synthase-1 has two glycosyltransferase activities: it acts as a GlcUA and a GalNAc transferase and is responsible for adding repeated disaccharide units to growing chondroitin sulfate chains.
  
  
  METHODS
  Recombinant wild-type chondroitin synthase-1 enzyme and the F362S mutant were expressed. These enzymes and cells expressing them were then characterized.
  
  
  RESULTS
  The mutant chondroitin synthase-1 protein retained approximately 50% of each glycosyltransferase activity relative to the wild-type chondroitin synthase-1 protein. Furthermore, unlike chondroitin polymerase comprised of wild-type chondroitin synthase-1 protein, the non-reducing terminal 4-O-sulfation of GalNAc residues synthesized by chondroitin N-acetylgalactosaminyltransferase-1 did not facilitate the elongation of chondroitin sulfate chains when chondroitin polymerase that consists of the mutant chondroitin synthase-1 protein was used as the enzyme source.
  
  
  CONCLUSIONS
  The chondroitin synthase-1 F362S mutation in a patient with neuropathy resulted in a decrease in chondroitin polymerization activity and the mutant protein was defective in regulating the number of chondroitin sulfate chains via chondroitin N-acetylgalactosaminyltransferase-1. Thus, the progression of peripheral neuropathies may result from defects in these regulatory systems.
  
  
  CONCLUSIONS
  The elongation of chondroitin sulfate chains may be tightly regulated by the cooperative expression of chondroitin synthase-1 and chondroitin N-acetylgalactosaminyltransferase-1 in peripheral neurons and peripheral neuropathies may result from synthesis of abnormally truncated chondroitin sulfate chains.
authors.affiliation: Department of Biochemistry, Kobe Pharmaceutical University, Higashinada-ku, Kobe, Japan.
authors.forename: Tomomi
authors.initials: T
authors.lastname: Izumikawa
authors.forename: Kazumasa
authors.initials: K
authors.lastname: Saigoh
authors.forename: Jun
authors.initials: J
authors.lastname: Shimizu
authors.forename: Shoji
authors.initials: S
authors.lastname: Tsuji
authors.forename: Susumu
authors.initials: S
authors.lastname: Kusunoki
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kitagawa
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002809:Chondroitin Sulfates / Q000378:metabolism*; D017931:DNA Primers; D006801:Humans; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D020125:Mutation, Missense; D017350:N-Acetylgalactosaminyltransferases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009422:Nervous System Diseases / Q000201:enzymology* / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid
chemical_list: D017931:DNA Primers; D002809:Chondroitin Sulfates; D017350:N-Acetylgalactosaminyltransferases; C412725:chondroitin synthase
keywords: CS; ChGn; ChPF; ChSy; Chondroitin sulfate; GalNAcT; GlcAT; Glycosaminoglycan; Glycosyltransferase; N-acetylgalactosaminyltransferase; Neuropathy; Proteoglycan; chondroitin GalNAcT; chondroitin polymerizing factor; chondroitin sulfate; chondroitin synthase; glucuronyltransferase; ΔDi-0S; ΔDi-4S; ΔDi-6S; ΔDi-diS(D); ΔDi-diS(E); ΔHexA(2S)α1–3GalNAc(6S); ΔHexA(α1–3)GalNAc; ΔHexAα1–3GalNAc(4S); ΔHexAα1–3GalNAc(4S, 6S); ΔHexAα1–3GalNAc(6S)